In-Field Resistance of REBCO Electrical Joints at 4.2 K Jerome Fleiter and Amalia Ballarino EuCARD WP10.2 EuCARD-2 is co-funded by the partners and the European Commission under Capacities 7th Framework Programme, Grant Agreement 312453

Introduction HTS splices for magnet application. Required: reproducible low electrical resistance high mechanical strength Use of soft solder for splicing (Sn-Pb and Sn-In) Three types of joints can be made between REBCO tapes Type 0 : direct facing of the HTS films (no substrates interleaved) Type 1: no direct facing of the HTS films (one substrate interleaved) Type 2 : no facing of the HTS films (two substrates interleaved) 4-12 mm 0.1 mm In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Conductors investigated Splices of Type 0,1 and 2 made from 4 mm wide conductors investigated at both 4.2 K (0.3-12.4 T) and 77 K (self field). Soft solder used: Sn-Pb for all except AMSC (Sn-In) Measurements reported as: splice resistance x surface (Sc (n cm2)) J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Splice resistance at 4.2 K (1/3) Type 0: lowest resistance 11.6 ncm2 for Bruker 36.1 n cm2 for SuperOx 36.2 n cm2 for SuperPower 152 n cm2 for AMSC 825 n cm2 for SUNAM* *measured excessive internal resistance on this batch Type 0 resistance almost unchanged (< 20%) vs. field and temperature (see next slides) J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Splice resistance at 4.2 K (2/3) Type 1 : ~7-16 times more resistive than Type 0 (except SuNAM) 98 ncm2 for Bruker (x8.6) 284 n cm2 for SuperPower (x7.8) 567 ncm2 for SuperOx (x16) 1138 ncm2 for SuNAM (x1.38)* 1092 ncm2 for AMSC (x7.2) *measured excessive internal resistance on this batch Type 1 resistance depends on field and temperature (see next slides) In-Field Resistance of REBCO Electrical Joints at 4.2 K J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Splice resistance at 4.2 K (3/3) Type 2: ~10-25 times more resistive than Type 0 (except SuNAM) 148 ncm2 for Bruker (x13.04) 371 ncm2 for SuperPower (x10.2) 884 n cm2 for SuperOx (x 24.5) 1396 n cm2 for SuNAM (x1.70)* 2127 n cm2 for AMSC (14.027) Type 2 resistance strongly dependent on field and temperature (see next slides) *measured excessive internal resistance on this batch J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Normalized change of Sc vs. B at 4.2 K Type 0 Type 1 Type 2 Type 1 and 2 joints strongly affected by field, not the case for Type 0 joints J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Splice resistance at 77 K and Lift Factor Ratio Type 0 : lift factor~1 => main contribution to Sc from conductor internal resistances Type 1 and 2 : lift factor 0.23-0.59 =>Part of the current circulates around substrate: Sc depends on copper properties RRR must be measured: on-going work Lift factor Sc(4 K)/Sc(77 K) Type 0 Type 1 Type 2 SuperPower 0.93 0.30 0.29 SuperOx 0.97 0.49 0.46 Bruker 1.29 0.24 0.23 SuNAM 0.92 0.37 0.35 AMSC 0.84 0.55 0.59 J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Conclusions Electrical resistance of REBCO lap joints characterized at 4.2 K versus field and at 77 K Three topologies of lap joint investigated: no substrates (Type 1), one substrate (Type 2) or two substrates (Type 3) interleaved in between the HTS layers. Lowest resistances measured for Type 0 at 4.2 K: 11.6 ncm2 for Bruker, 36 ncm2 for SuperPower and SuperOx tapes 151 ncm2 for AMSC tapes. 825 n cm2 for SUNAM (excessive value, could be smaller) Type 0 resistance almost unchanged (<20%) vs. field and temperature Type 1 joints: 7-16 times more resistive compare to Type 0 (except SuNAM*) Type 2 joints 10-25 times more resistive compare to Type 0 (except SuNAM*) On-going work: RRR measurement of Cu stabilizer Characterization of 12 mm wide splices * measured excessive internal resistance on this batch J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Back Up In-Field Resistance of REBCO Electrical Joints at 4.2 K J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015

Back Up In-Field Resistance of REBCO Electrical Joints at 4.2 K J. Fleiter and A. Ballarino, "In-Field Resistance of REBCO Electrical Joints at 4.2 K”, CERN internal note 2015-10 , EDMS Nr: 1562549. In-Field Resistance of REBCO Electrical Joints at 4.2 K EuCARD2, WP 10.2 meeting CERN, 1st December 2015